(a) Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device. More particularly, the present invention relates to a method of forming a gate pattern having a small critical dimension using an ArF photoresist as an etching mask.
(b) Description of the Related Art
As semiconductor devices become smaller, faster and more integrated, photolithography and etching processes become more critical in fine patterning of the devices. The photolithography and etching processes typically comprise forming a photoresist pattern and selectively removing portions of a target layer thereunder using the photoresist pattern as an etching mask so as to form a predetermined pattern in the target layer, for example a gate electrode pattern. The photoresist pattern is generally formed by a sequential process including coating a photoresist on a layer to be etched, exposing the photoresist by passing light of a certain wavelength or wavelength band through an exposure mask, and removing the exposed (or unexposed) photoresist with a solvent.
A critical dimension (CD) obtained by the photolithography process depends on the wavelength of a light source in the exposure process. For example, a light source with a shorter wavelength may be beneficial for a patterning a photoresist layer of a finer line width.
Conventionally, a KrF light source is used for forming a photoresist pattern, but patterning a fine line having a width narrower than 130 nm is difficult when using the KrF light source. Therefore, an ArF light source that has a narrower wavelength and a higher resolution than the KrF light source has recently been used for the exposure process. In addition, a photoresist material having a high resolution with the ArF light source, that is, an ArF photoresist, has been used for the exposure process.
In a photolithography process using the ArF exposure light source, a bottom anti-reflection coating (BARC) for preventing a diffused reflection is firstly formed on a target layer such as a gate electrode layer. Thereafter, an ArF photoresist is coated on the BARC, and the ArF photoresist is exposed to light from an ArF light source passed through a reticle and developed so as to form a photoresist pattern. In addition, after the target layer is etched using the photoresist pattern as an etching mask, the photoresist pattern is removed.
However, there are some difficulties even if the ArF photoresist is used, that will be described hereinafter.
In etching a polysilicon layer, the photoresist pattern linewidth should be narrower than 80 nm for forming a gate pattern having a design rule (or critical dimension) of 65 nm. In this case, as an aspect ratio of the photoresist pattern increases, the photoresist pattern may easily collapse, and the line edge roughness may increase, so that a process window for a depth of focus (DOF) decreases.
In addition, in patterning a gate pattern having a critical dimension (after etching) of about 65 nm using an ArF photoresist, the wavelength of light from the ArF light source is shorter than that from the KrF light source, so that a thickness (2000-2700 Å) of the ArF photoresist should be smaller than a thickness (3000-3500 Å) of the KrF photoresist. Moreover, the ArF photoresist has a hardness that is lower than that of the KrF photoresist, so that the photoresist pattern may be easily distorted by plasma generated in an etching process. As a result, the difficulties in using the ArF photoresist may cause a pattern failure.
In order to overcome those difficulties, an etching process condition where a difference between a critical dimension (CD) before an etching process and a CD after the etching process can be 30-40 nm should be developed, but this has not been satisfactorily proposed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention. Therefore, it may contain information that does not form prior art or other knowledge that is already known in this or any other country to a person of ordinary skill in the art.